It's no secret that the human body is the most complex "machine" ever created. It has an operating system. If you fail to obey the rules of that operating system, you will break--sickness, injury, disease, and even death.
The "secret" then is finding the answer to the question, "How do you take care of your body with the least amount of short-term AND long-term cost to you?" Because ultimately, you will pay for your health, either now or later--through an intelligent, proactive fitness program, or through thousands of dollars in co-pays for medications and medical treatments.
The answer to that question is that you need a program, not a workout, that "undoes" all that your body has been through--the stiffness from lack of moving; you need a program that strengthens all the muscles that are designed to move, but don't; you need a program that not only strengthens you heart, but protects it from disease and the trauma of a heart-attack; you need a program that helps you be the absolute best you can be at whatever it is you do.